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BUREAU OF MINES 
INFORMATION CIRCULAR/1989 




Computer-Assisted Continuous 
Coal Mining System-Research 
Program Overview 

By George H. Schnakenberg, Jr. 



UNITED STATES DEPARTMENT OF THE INTERIOR 



Mission: As the Nation's principal conservation 
agency, the Department of the Interior has respon- 
sibility for most of our nationally-owned public 
lands and natural and cultural resources. This 
includes fostering wise use of our land and water 
resources, protecting our fish and wildlife, pre- 
serving the environmental and cultural values of 
our national parks and historical places, and pro- 
viding for the enjoyment of life through outdoor 
recreation. The Department assesses our energy 
and mineral resources and works to assure that 
their development is in the best interests of all 
our people. The Department also promotes the 
goals of the Take Pride in America campaign by 
encouraging stewardship and citizen responsibil- 
ity for the public lands and promoting citizen par- 
ticipation in their care. The Department also has 
a major responsibility for American Indian reser- 
vation communities and for people who live in 
Island Territories under U.S. Administration. 



Information Circular 9227 

Computer-Assisted Continuous 
Coal Mining System-Research 
Program Overview 

By George H. Schnakenberg, Jr. 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Manuel Lujan, Jr., Secretary 

BUREAU OF MINES 
T S Ary, Director 




u* ^ 



1 



tf' 



Library of Congress Cataloging in Publication Data: 



Schnakenberg, George H. 

Computer-assisted continuous coal mining system-research program overview / 
by George H. Schnakenberg, Jr. 

(Information circular / Bureau of Mines; 9227) 

Bibliography: p. 15 

Supt. of Docs, no.: I 28.27: 9227. 

1. Coal-mining machinery-Data processing. 2. Robots, Industrial. 3. Coal- 
mining machinery-Data processing-Research. 4. Robots, Industrial-Research. I. 
Title. II. Series: Information circular (United States. Bureau of Mines); 9227. 

TN295.U4 [TN813] 622 s-dcl9 [622\334] 89-600048 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Research facilities 3 

Fundamental research 3 

Background 3 

Activities and status 3 

Technology development 4 

Objective and approach 4 

Target system 4 

Intelligent control 4 

Intelligent tasks of extraction 4 

Basic machine 5 

Background 5 

Activities and status 5 

Computer system 6 

Background 6 

Activities and status 6 

Machine control 8 

Background 8 

Activities and status 8 

Guidance systems 8 

Background 8 

Activities and status 9 

Coal interface detection 12 

Background 12 

Activities and status 12 

Machine diagnostics 13 

Background 13 

Activities and status 13 

Planning 14 

Background 14 

Activities and status 14 

Summary 15 

References 15 

ILLUSTRATIONS 

1. Technology evolution of intelligent mining systems 2 

2. Computer functions for intelligent machines 6 

3. Computer network and components, 1988 7 

4. Mobile roof support 10 

5. Integrated navigational and guidance system concepts 11 

6. Locomotion emulator 12 

TABLE 

1. Intelligent mining machines-critical systems and technologies 5 



UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


cm 


centimeter 


MHz 


megahertz 


ft 


foot 


m 


meter 


Hz 


hertz 







COMPUTER-ASSISTED CONTINUOUS 

COAL MINING SYSTEM-RESEARCH 

PROGRAM OVERVIEW 



By George H. Schnakenberg, Jr. 1 



ABSTRACT 

Automation of coal mining activities at the face offers improvements in worker safety, health, and 
productivity. Introduction of integrated computer-sensor systems to current mining machines will enable 
these machines to perform some of the most hazardous tasks through supervised teleoperation. The 
U.S. Bureau of Mines is pursuing the development of the enabling technology necessary to achieve this 
goal. The research program consists of both basic and applied research, each focused on the fun- 
damental issues of computer and sensor technologies. Short-term research is directed to providing 
computer-assisted, remote supervisory operation of present underground equipment; the long-term goal 
is the development of progressively more intelligent mining systems. 

The research program includes a review of robotic machine and autonomous vehicle technologies and 
of current mining technology, which provides a base for developing innovative mining methods; research 
in navigation and guidance technology, emphasizing control of a continuous mining machine; research 
on coal-rock interface sensing technology for horizon control, and rib thickness control in highwall 
mining; the development of computer systems and hierarchical architectures for real-time control; and 
development of expert systems for machine system fault diagnostics and predictive maintenance. This 
report presents a brief background and the current status for each of these research areas. 



Research physicist, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



The U.S. Bureau of Mines has initiated significant new 
thrusts in mining research that focuses on creating signif- 
icant breakthroughs in mining technology that are required 
to substantially improve worker health, safety, and effi- 
ciency, while also increasing the international competitive- 
ness of the U.S. mining industry. The application of 
automation and computer technologies to coal m inin g can 
make substantial and simultaneous contributions to worker 
health, safety, and mining productivity, as measured in 
terms of human, capital, or resource utilization. Because 
the mining industry and its manufacturers and suppliers 
are individually unable to perform the extensive high-risk 
research needed, the task of performing the research falls 
on the Bureau. 

To optimally conduct the program, the research must 
be planned carefully and must be performed in close rela- 
tion with private, government, and academic researchers in 
the space, armed forces, and factory automation and 
robotics research areas, and with the close cooperation of 
both labor and management of the mining industry. 

The resulting research program to develop intelligent 
mining systems is a mixture of basic research, applied 
research, information gathering, and the application and 
adaptation of existing technologies from a multitude of 
sources. It was devised through an examination of the 
basic elements of coal mining while weighing factors such 
as worker exposure to hazards, greatest potential produc- 
tivity increases to be gained, the application to existing and 
future coal mining methods, the depth and extent of uni- 
versality and applicability of research issues involved, and 
the degree to which it increased the Bureau's knowledge 
of the fundamental technologies in computer-assisted 
machine control systems and mining. The research pro- 
gram contains (1) elements that are of a general nature, 
(2) elements that are focused on a specific system design 
and objectives, and (3) ad hoc elements that address a 
particular mining problem. All of the elements blend 
together to form a coherent effort to develop the requisite 
enabling technology for successful intelligent coal mining 
systems (fig. 1). 

The development of intelligent mining systems 
encompasses a wide range of issues. Rather than take a 
breadth-first approach and consider all of the issues, the 
research plan takes a depth-first approach on the three 
fundamental issues of extractive mining-releasing the coal 
from the host rock, transporting the extracted material to 
the surface, and control of the ground. The major, near- 
term efforts focus on extraction. Other essential elements 
of mining are maintenance of equipment, provision and 
transport of supplies and equipment services such as power 
and water, environmental control, and mine planning and 
management. 

Extraction activities present the most hazards to 
workers, experience substantial idle and delay times, and 



provide a wealth of research areas that can be broadly 
applied to the other essential elements of underground 
mining. Therefore, the Bureau's research is focused on 
developing an autonomous extraction machine. 

Highly mobile coal mining machines, as exemplified by 
the continuous mining machine, will have a significant role 
in the future of coal mining; they will serve as the major 
method for longwall development, room-and-pillar mining, 
shortwall mining in a variety of roles, and in highwall 
mining. 

The robotic technology developed for this research 
machine and the associated mining system can be utilized 
in other mining equipment and provides the basis for the 
development of novel mining systems that take specific 
advantage of the advanced technology. The subsystems 
developed can be utilized individually in the near term as 
aids to remote-controlled continuous mining or in 
extending further the automation of longwall mining 
systems. 

The research is divided into three categories: (1) a 
fundamental or core program of research that explores and 
develops the fundamental knowledge and hardware, (2) an 
applied research program that brings the pieces or in- 
tegrated systems to a demonstrable, reliable, and 
fieldworthy stage, and (3) ad hoc solutions to mining 
industry needs. This report presents a review of this 
research by giving a brief description of the Bureau's 
research facilities; a discussion of the fundamental research 
effort, an introduction to the technology development-the 
applied research program and the major research effort, 
and the background and current status for each of the 
elements within the technology development program. 



1988 



1995 



2000 
i 



FUNDAMENTAL INVESTIGATIONS 



^ 




TECHNOLOGY DEVELOPMENT 

Task planning 

Modeling- simulation cmaqi iur~~ 

Machine diagnostics -rrrufjninrv 

Coal seam detection TECHNOLOGY 

Guidance Navigation ^s 

Machine control 



NEW MINING 
TECHNOLOGY 



Computer systems 

-Basic machine Advanced machines 

FIELD PROTOTYPE TECHNOLOGY 





INDUSTRY APPLICATIONS 



Figure 1 .-Technology evolution of intelligent mining systems. 



RESEARCH FACILITIES 



The research on computer-assisted mining systems is 
being conducted at the Bureau's Pittsburgh Research 
Center located at Bruceton, PA, a few miles outside of 
Pittsburgh. Located at this site is a mining equipment test 
facility (METF), a complex of large, spacious buildings 
that house the Bureau's experiments involving full-size 
mining equipment. Included in this facility is a Joy 16CM 2 
continuous mining machine, which serves as the temporary 
research test bed for the autonomous mining research. 
Adjacent to it is a 6-ft-high block of coalcrete, an artificial 
coal used for testing various mining and drilling systems. 
In the same area will be the Carnegie Mellon University 
(CMU) Locomotion Emulator, or navigation research 



platform, a mobile vehicle that is software configurable to 
emulate the motions of any type of wheeled or tracked 
vehicle. A trailer with a large viewing window houses the 
computers and terminals from which either the continuous 
miner or the LE is operated for research experimentation 
or visitor demonstrations. An ethernet network (a form of 
local area network for intercomputer communication) 
connects the computers in the trailer to the research 
laboratories and offices located in another building. The 
computer facilities utilized for this program include five 
Sun workstations, a Symbolics 3670, and numerous per- 
sonal computers (PC's) and terminals. 



FUNDAMENTAL RESEARCH 



BACKGROUND 

The major role of the Bureau's fundamental research 
program is to provide a resource of computerized machine 
control systems and mining technologies by assembling 
information. The resource information covers robot- 
specific components and systems in areas such as sensing 
and vision, manipulation, control, and locomotion. Mining 
technology and methods are also being investigated and 
documented. The resource information will be kept cur- 
rent and used as reference and familiarization material. 
The enabling technology developments from Bureau re- 
search will be included as well. This effort will also be 
used as a means to conceptualize novel mining methods by 
using a systems approach to coal mining given the 
combined capabilities of robotic and advanced mining 
technologies. 

This program is also investigating hardware and 
software for the intelligent control of mining machines. 
Bureau-sponsored work at the National Institute of 
Standards and Technology (NIST) [formerly known as the 
National Bureau of Standards (NBS)], Robot Systems 
Division, will capitalize on NIST's experience in control 
systems developed for the NIST Automated Manufacturing 
Research Facility (i) 3 and adapted for the National 
Aeronautical and Space Administration (NASA) as 
NASA/NBS Standard Reference Model (NASREM) 
Architecture for the Space Station Telerobot System (2). 
Over the next 3 years, NIST will develop a Mining 
Automation Standard Reference Model (MASREM) 
starting with the development of a concept document, a 
design model using a new, advanced modeling tool, and a 
mining simulator requirements specification that will be an 
adaptation of NIST's simulator used for the multiple 



— *— — 

Reference to specific products does not imply endorsement by the 

U.S. Bureau of Mines. 

Italic numbers in parentheses refer to items in the list of references 

at the end of this report. 



autonomous underwater vehicle developed for the 
Department of Defense. 

Also included in the fundamental research is Bureau- 
sponsored work at CMU under contract HO358021, 
"Robotic Sensing and Control for Underground Mining." 
After having examined several options, researchers at 
CMU have decided to pursue the implementation of 
strategic planning in Smalltalk-80, an object-oriented 
programming language. Strategic-level planning uses 
reasoning to make the major decisions involved in the 
mining of an entry. It uses the knowledge of the mine 
plan, the relationship of the machine to the surrounding 
geometrical and geological environment, and similar levels 
of knowledge, to formulate subgoals for the mining 
machine. For example, the strategic-level planner is con- 
cerned with determining where the machine is to move or 
mine next but not with how it is to perform the moves or 
the cutting; these planning tasks are left to lower levels in 
the control hierarchy. CMU is also developing a means to 
generate a representation of mine ribs and corners (the 
point or line representing the intersection of ribs or a rib 
and the face) using occupancy grid models in conjunction 
with ultrasonic range data. 

The essence of the NIST and CMU activities is to 
investigate the fundamental issues involved in the 
hierarchical control of mining equipment activities and to 
provide the Bureau with a structured approach and 
structured software systems in which to implement the 
control of the Bureau's research test bed, the continuous 
mining machine. Duration of these programs is 3 or more 
years, starting from 1988. 

ACTIVITIES AND STATUS 

Resource information on robotic systems technology has 
been assembled for electrical actuators and mechanical 
mechanisms for manipulators, sensors used in robotics, 
diesel power for locomotion, and ventilation and dust 
control systems. CMU has explored rudimentary planning 



of continuous miner moves using the "knowledge" of miner 
location, face and rib locations, and mining objective. The 
work is being done in Smalltalk-80 on the Bureau's Sun 3 
workstation. The miner and mine entries are graphically 
represented in order to visually show results of the 
program's operation. A means to communicate machine 



commands that move the Smalltalk-80 screen picture of 
the miner to the real machine via a standard RS232 com- 
munications link has been developed in preparation for 
eventual machine control. Work is continuing on 
expansion of the program beyond the prototype stage, 
including occupancy modeling using ultrasonic range data. 



TECHNOLOGY DEVELOPMENT 



OBJECTIVE AND APPROACH 

The objective of the technology research is to develop 
and evaluate the enabling technology for autonomous 
mining systems. The Bureau's approach is to select a 
target system that attacks the major mining safety and 
productivity improvement goals that provide opportunity 
for incremental advances and thus supports the slow, 
evolutionary introduction of technology into mining, and 
whose results are not limited to only the target system 
itself. Such a focused approach provides the researchers 
with tangible objectives and can show demonstrable results 
throughout the evolution of the technology. 

TARGET SYSTEM 

The target machine for this research is the rather 
universally used continuous mining machine. Its control 
and operational characteristics are representative of the 
class of high-mobility extraction machines used in coal 
mining for longwall entry development, room-and-pillar 
mining in advance and retreat, shortwall mining, and the 
like. Using this machine as the target machine exposes a 
large number of research issues and allows incremental 
introduction of intermediate developments. 

INTELLIGENT CONTROL 

The Bureau is careful to make the distinction between 
automation and autonomous or between programmed and 
intelligent control. In the first case, a machine is con- 
trolled by a fixed script or command list that is executed 
in a fixed order. The target values for the machine and its 
appendage positions are placed in a list and executed in 
order without alteration. Intelligent control alters or 
rewrites the script based upon the analysis of the current 



circumstances derived from sensor data and a programmed 
knowledge base. It is the use of current circumstances, 
including human operator input, to alter the next and 
subsequent machine actions that makes the machine intel- 
ligent and thus able to operate autonomously. It is appro- 
priate to note that the analysis and alteration process can 
take place at differing levels of complexity, from a 
relatively simple situation in which the mining forces are 
too great so that the cutting rate slowed down (force 
cognitive feedback) to a rather complex situation in which 
a roof fall or geological anomaly results in the changing of 
the mining position and cutting sequences. Also the 
reaction times vary with the differing levels of control, 
generally with a quicker response needed for the simpler, 
lower level control. The natural result is a hierarchical 
control structure. 

INTELLIGENT TASKS OF EXTRACTION 

An examination of the actual functions that a machine 
operator must perform in order to extract coal discloses 
the key research and development topics critical to the 
development of an intelligent mining machine. The oper- 
ator must guide a cutting machine tool within a coal seam 
following apian that can be altered by local conditions and 
events. These key words, machine, guide, within coal, 
plan, and altered, form the guiding structure to the 
Bureau's development of enabling technology. Tying all of 
these functions together is a backbone of data gathering 
and information processing residing in a complex computer 
system. It is the computer system and software that 
embodies the human operator's capabilities. The result is 
a list of critical path technology categories shown in 
table 1. This list is the guide for the discussions in the 
remainder of this report. 



Table 1 .-Intelligent mining machines-critical systems and technologies 



System 

Basic machine . . . 
Computer system . 

Machine control . . 



Guidance systems 



Dominant components 
and issues 

Mechanical, electrical, 
hydraulic. 

Processor boards, 
operating system; 
communication networks 
for real-time 
multiple-processor 
operations. 

Position, electrical, 
hydraulic sensors; 
computer data 
acquisition, 
closed-loop control 
algorithms, 
command language. 

Position and heading 
sensors and systems; 
obstacle and mine 
rib detection and 
registration to map 
data; computer software 
for data fusion and 
filtering. 



System 



Coal interface 
detection. 



Machine diagnostics 



Planning 



Dominant components 
and issues 

Coal and strata 
properties and 
differences; 

multidisciplinary systems 
for real-time sensing 
of cutting positions; 
artificial intelligence 
data interpretation. 

Sensors of machine 
condition; expert 
system interpretation 
and analysis; human 
interfacing. 

Data interpretation, 
knowledge representation, 
artificial intelligence, 
human interfacing. 



BASIC MACHINE 



BACKGROUND 

A typical mining machine is an assembly of mechanical, 
electrical, and hydraulic systems working together to form 
a machine with certain functions and operating characteris- 
tics. In general, machines in mining are not automated 
nor configured for computer-controlled operation, and thus 
each one must be modified for closed-loop control. That 
is, all parts normally controlled by the operator to perform 
work-the appendages and means of propulsion-must be 
retrofitted with actuators that respond to the electrical 
signals from the controlling computer. The appendages 
must be retrofitted with sensors that report to the 
computer the position of the appendage with respect to the 
machine. The basic machine system is strictly concerned 
with the hardware and its selection, design, and operating 
characteristics. 

The computer-driven actuator-machine-sensor system 
must be fully studied in order to characterize its behavior 
in detail in preparation for the development of algorithms 
for closed-loop control. The machine systems possess 
operating capabilities and limitations in terms of mobility 
and functional performance; these must be fully 



characterized to be used as data for path planning and 
task planning software. 

In the final prototyping stages in preparation for 
in-mine testing, attention must be given to electrical 
permissibility (for use in gassy mines) and safety. Sensors 
for diagnostic machine condition monitoring must be 
selected, installed, and tested, and data must be gathered 
on normal and abnormal conditions. 

ACTIVITIES AND STATUS 

The Bureau-owned Joy 16CM continuous mining ma- 
chine is being used as the test bed for the initial testing 
and evaluating of sensing and control systems. Sensors for 
appendage movement, the electrical system (voltage and 
current), and the hydraulic system (pressure, temperature, 
flow, debris, and fluid level) have been selected, installed, 
and interfaced to the computer. The computer has been 
interfaced to the electrically actuated hydraulic control 
valves for appendage movement and to the control relays 
for the crawler tracks. 

Appendage motion and control characteristics have 
been obtained (3). Locomotion response characteristics as 
measured by onboard sensors were obtained only recently. 



COMPUTER SYSTEM 



BACKGROUND 

The computer system forms the backbone of the 
machine control system for any autonomous, intelligent, or 
robotic machine. At the lowest level it handles the closed- 
loop control of the various appendages. In this role it 
takes data from the appendage position sensor, compares 
these values with the target value desired, and initiates, 
maintains, or stops appendage movement as necessary. At 
the highest level it will perform complex planning of 
machine goals: the sensor data that were abstracted are 
compared with the goals represented in suitable form, and 
an ordered list of subgoals is generated. A model of the 
computer functions is presented in figure 2. 

As a practical matter, the computer system must grow 
with the project. Although the complexity of the final 
system is somewhat predictable, the rate at which 
computer capabilities are changing effectively limits the 
investment in a system to that which is not much more 
complex than is needed to support approximately 2 years 
of research. The computer system should support multiple 
processors and/or computers, provide access to machine 
control primitives (e.g., shear up 10 cm) from any level of 
processor or computer, provide access to system variables 
from any level, support real-time control, provide an 
environment for experimentation and development using 
heterogeneous computers, provide flexibility and extend- 
ibility, and use off-the-shelf hardware. 

ACTIVITIES AND STATUS 

The computer system consists of a central control and 
data acquisition computer mounted on board the mining 
machine (4). It is an Intel 80286 processor-based system 
running Intel's iRMX86 real-time, multitasking operating 
system. The software is written in PL/M-86 and provides 
a menued interface at a terminal for keyboard control of 
the mining machine functions. Individual machine func- 
tions and motion can be selected, and target values or 
operational durations can be set and executed. A script 
writing, editing, and execution mode is also provided to aid 
research, evaluation, and demonstration. Closed-loop 
control of the appendages is performed solely by this 
computer. This computer provides the foundation and the 
low-level control functions of the machine control hierar- 
chy. It is also the primary means for data acquisition from 
the sensors on the hydraulic and electrical systems for 
condition monitoring and diagnostics. A magnetic bubble 
memory cartridge substitutes for floppy or hard disk mass 
storage media and provides the operating software for the 
system. 

The computational requirements for an intelligent ma- 
chine far exceed those of a single, multitasking computer. 
Several processors and/or computers will be required and 
must be able to share data and have access to the machine 



control commands and sensor data. A real-time control 
network of heterogeneous computers is required. The 
Bureau has chosen to use the Intel BITBUS distributed 
control environment, which is a polled, high-speed, secure 
communications network operating over twisted pair wires. 
Each computer or processor connects to the network 
through a node interface card, itself a small dedicated 
computer. The separation between nodes can exceed 
several hundred feet. 

Although this system uses off-the-shelf components and 
software, the actual implementation and customization of 
the operating system and BITBUS network is not trivial. 
At this point, the BITBUS network is configured and fully 
operational; it is capable of supporting the Bureau's 
development for the next 2 years or more. 

At the present time, a 10-MHz, single-board computer 
programmed in BASIC for gyroscope heading control, a 
Sun 3/60 workstation programmed in C for the laser-based 
guidance system, a Sun 4/110 color workstation also 
running C programs under UNIX for a system view port, 
a Sun 3/160 functioning as a planner, and a Symbolics 
3670 color computer, running LISP and displaying hy- 
draulics system status graphically, are attached to the 
BITBUS network. The system is shown in figure 3. 

Within the next year the network will expand to include 
an elementary form of wall and face recognition, location, 
and mapping using ultrasonic ranging sensors; elementary 
path planning and cutting sequencing; and condition 
monitoring and diagnostics. Each will be running on its 
own workstation. This system is complex as it is being 
used for research and development. A final delivery 
system will utilize several compact but high-powered 
single-board computers. 



System 
view ports 

Data fusion 



HUMAN 
WORLD 



Storing 
Processing 



L INTELLIGENCE 



Interpretation 



DATA 



Modeling 



1 Facts and 
goals 



Planning 



Decisions 



Acquisition ., COMMUNICATIONS Primitive commands 



SENSORS 



Simulations 



Task lists 
Command lists 



MACHINES 



PHYSICAL 
WORLD 



ACTIONS 



Simulations 



Figure 2.-Computer functions for intelligent machines. 



BITBUS NETWORK 



JOY 16 CM- 



BCC-52 



Gyroscope, 

compass, clinometers 

Heading control 
loop 



INTEL 80286" 



MACHINE CONTROL 

Appendage control 
loops 

Motion actuators 

Electrical and 
hydraulic sensor 
data acquisition 



SUN 3/60 

LASERNET 

Position and heading 

sensor processing 

and control loop 



.J 



TERMINAL 



VOICE CONTROL 



| Bitbus node 



-SUN 3/160- 
PLANNER 

(Smalltalk) 

Strategic and 
tactical moves 



— SUN 4/110 — 
VIEW PORT 

Machine graphics 
Sensor graphics 

Sensor logging 
Manual control 



■SYMBOLICS 3670 

Hydraulic system 
graphics 



Figure 3.-Computer network and components, 1988. 



MACHINE CONTROL 



BACKGROUND 

Machine control represents an integration of the 
machine hardware, position sensors, and control computer 
systems. It is this element in the development that results 
in a machine that accurately executes commands contain- 
ing target values; i.e., a machine that is operating under 
closed-loop control. In closed-loop control, a function is 
named and a target value specified. These target values 
are either a destination position, a specified change in 
position, or a duration for a particular function. The 
control computer creates a task to issue a signal to the 
machine actuator (solenoid on a hydraulic valve) and 
another task to continuously read the output from the 
sensor reporting the position of the appendage being 
actuated. The sensor output is compared with the target 
value using an algorithm developed to optimize function 
performance. When the specified target value and sensor 
output agree according to the comparison algorithm, the 
computer shuts off the signal to the machine actuator. 
The computer is also able to accept a halt command to 
stop any actuation before it is completed. This system is 
described in detail in reference 3. 

Safety issues must also be considered. A computer 
malfunction or crash could cause a machine shutdown; 
systems must be developed to avoid this problem. 

At a higher level of control, the forces on the machine 
components, sensed in the form of increased motor 
current or hydraulic pressures, can be used as part of the 
control loop, primarily to prevent damage to the machine. 
These forces could also be used to indicate changes in 
geology and used to alter a cutting sequence, for example. 

The generalized tasks involved in sensor-based machine 
control are as follows: Select a sensor for the controlled 
appendage function; develop the computer-sensor and 
machine-sensor interface; test the machine and sensor 
system; analyze the data; formulate control algorithms; 
test control in free space; test in simulated mining 
conditions (artificial coal); analyze data; repeat 
development, testing, and analysis as necessary. 

ACTIVITIES AND STATUS 

All the development, test, and analysis tasks have been 
completed for the position sensors for all movable 



appendages and the crawler tracks on the Bureau's test 
bed mining machine. Thus the shear elevation, gathering 
head elevation, conveyor swing, conveyor elevation, and 
stabilizer jack elevation have been placed under closed- 
loop computer control. The crawler tracks are not under 
closed-loop control using crawler movement sensors, nor 
will they be, since crawler slippage with the ground renders 
measurement of crawler travel useless as data for precise 
control of machine position. 

Over 2,700 graphs of machine appendage response data 
were generated and cataloged in the computer-machine- 
sensor response testing phases. Analysis of this infor- 
mation enabled the formulation of control algorithms, 
verification of sensor operation, and determination of 
parameters for control fault detection. Tests for shearing 
arm elevation control were performed in coalcrete, an 
artificial coal consisting of a mixture of fly ash, coal, and 
cement. The shear drum height can be controlled to 
within 1 cm. 

At this point the machine is computer controlled and its 
appendages are controllable to any specified position in the 
operating range. The locomotion is not yet under closed- 
loop control. The research for closing the loop on the 
locomotion is being performed under the navigation and 
guidance element, presented in the "Guidance Systems" 
section. 

The development of machine control is not finished 
even though the work to date has been successful. To 
move the control from the test bed to a real machine in a 
real mine, additional work is anticipated including im- 
provements of the control accuracy; i.e., the development 
of adaptive control in which changes in machine and 
sensor characteristics are compensated for dynamically. 
Additionally, a special effort must be made in error and 
fault detection to provide a check on vital machine 
functions and conditions prior to machine operation, 
provide autocalibration of position control sensors, and 
devise software to detect and prevent runaway motions. 
The hardware complexity and cost must be reduced to 
minimize production costs. 

Under this research element, 20 diagnostic sensors have 
been mounted and interfaced to the computer on board 
the continuous mining machine. The data from these 
sensors are available to the condition monitoring and 
maintenance diagnostic systems being developed. 



GUIDANCE SYSTEMS 



BACKGROUND 

Navigation and guidance is one of the most critical 
elements in the development of safer and more productive 
mining equipment that can operate without human 
presence in hazardous areas. Without an adequate means 



of self-guidance, too much human interaction and presence 
will be needed for machine control. 

Extraction machine guidance falls naturally into two 
divisions-lateral and vertical. The first refers to position- 
ing the machine laterally within the open spaces of an 
entry, and the latter refers to keeping the machine within 



the coal seam and maintaining the extraction to given 
tolerances and dimensions relative to the overlying and 
underlying strata. Vertical guidance is so fundamentally 
different from lateral guidance it is treated as a separate 
research issue. This section discusses only lateral guidance 
research. 

The Bureau has divided the lateral navigational problem 
into three domains: the face area, the section, and the 
whole mine. It was decided that the face area was most 
important for research at this time, and that when that 
problem was solved, navigation and guidance within the 
section and throughout the mine would be relatively easy. 
The Bureau is also working on the guidance of deep- 
penetrating highwall mining machines, which in addition to 
staying within the coal seam must be laterally guided to 
maintain the rib thickness to within certain tolerances 
dictated by maximizing recovery and maintaining sufficient 
ground control. 

Face navigation and guidance research are concerned 
with determining how a machine moves from place to 
place, or how it positions itself for doing a function and 
not with why the moves or positioning occurs, the latter 
being a higher level planning task. The research deter- 
mines the sensing systems, the interpretation and rep- 
resentation of sensor information for obstacle avoidance 
and motion planning, the extent of knowledge of machine 
locomotion characteristics, and the intelligent software that 
integrates all these things to produce an ordered list of 
elemental machine move commands. 

The inputs to the navigation and guidance system are 
the coordinates and heading to be reached that are within 
the sensing system's range of knowledge (visual horizon); 
the output is one or more elemental machine moves that 
will place the machine at this position and heading without 
having any part of the machine collide with the ribs or 
known obstacles. For a continuous mining machine using 
crawler tracks as the means of locomotion, these elemental 
commands are forward fast or slow, backward fast or slow, 
turn left or right with opposite track forward, turn left or 
right with opposite track reverse, pivot turn left or right. 
While the machine moves, the sensor visual horizon moves 
with the machine, the knowledge is updated, and the move 
list generation process continues. 

Guidance at the face requires sensing systems to 
provide machine location coordinates (x,y), the machine 
yaw (heading), the location of obstacles such as ribs and 
face, and the corners formed by the intersection of two 
ribs or ribs and face. For accurate closed-loop control of 
the elemental moves, machine location and heading must 
be acquired sufficiently fast. The machine pitch and roll 
and the location of the roof may be required. All of the 
guidance sensor information must be in a form from which 
machine moves can be planned, machine positioning at the 
face for cutting can occur, and maps can be constructed or 
updated based on knowledge of machine location in the 
mine coordinate frame as the coal is removed. 



ACTIVITIES AND STATUS 

Accurate knowledge of the mining machine's position 
and orientation in the mine coordinate system is needed in 
order to mine according to a set mine plan. The absence 
of features in the mine ribs at the face precludes the use 
of feature recognition techniques. Because crawler track 
slip on the floor precludes the use of dead reckoning 
odometry methods, an external reference structure that 
can be accurately located in the mine and from which the 
machine location can be determined was deemed neces- 
sary. The existence of the mobile roof support— the open 
rectangular structure shown in figure 4-suggested its use 
as a suitable reference frame for initial research. A 
mobile roof support adds "features" to the mine ribs that 
may be detected by ultrasonic ranging, and can support 
other active or passive devices for determining the range 
and heading of the mining equipment operating in its 
vicinity. The structure could also have additional functions 
such as supporting the roof, handling electrical cables and 
water hoses, supporting ventilation tubing and dust 
scrubbing devices, making environmental measurements 
for methane and air flow, and providing a vibration-free 
location for control computers, to name just a few. 

The Bureau's first iteration in guidance system 
development uses commercially available, off-the-shelf 
sensors. The present configuration for research and 
development of machine guidance uses multiple laser- 
based scanners for determining the position (x,y) and 
heading angle with respect to the control structure on 
which the scanners are mounted. A gyroscope for short- 
term control of machine heading relative to a previous 
heading, a fluxgate compass for heading relative to 
magnetic north, and clinometers for pitch-and-roll angles 
relative to gravity are mounted on the mining machine. 
Ultrasonic ranging is being investigated for indicating the 
position of ribs and concave and convex corners. 

The laser scanner method for determining position and 
heading as described in reference 5 works as follows: The 
Lasernet, a commercially available device, scans a 
horizontal plane at 20 Hz for retroreflective targets within 
its 30-ft range and 90° field of view. Upon request, it 
reports the angular position of the detected targets. When 
multiple targets (at least three for a single laser scanner, 
at least two for two laser scanners) are arranged in a 
known, fixed geometry, the location and position of the 
target arrangement can be determined by triangulation 
solely from their angles as reported by the laser. When 
the targets are mounted on a piece of mining equipment, 
the location and heading of the equipment are determined. 
The range of the laser scanner can be increased by using 
a more powerful laser and more sensitive detectors. 

At the present time, the laser system, gyroscope, and 
fluxgate compass are being individually evaluated for 
performance and accuracy. The control and analysis 
software is being written. Initial indications are that the 



10 




Figure 4.-Mobile roof support. 



laser scanners have adequate angular resolution but limited 
range. The software for target recognition and position 
and heading calculations has been written in high-speed 
(10 MHz) BASIC on a commercially available single-board 
computer. This BASIC language has proven to be too 
slow and the software is being rewritten in C on a Sun 
workstation. The work with the gyroscopes and fluxgate 
compass is discussed in reference 4. 

The ultrasonic ranging devices are Polaroid transducers 
that have been thoroughly investigated only recently for 
their response to real mine surfaces. CMU is currently 
investigating the use of the limited resolution sonar data 
for the generation of mine geometrical features using 
occupancy modeling. There is some question whether 
Polaroid transducers produce data with sufficient 
resolution to make feature determination possible. 

Because of the individual limitations of each of the 
selected sensing systems, the present concept for sensor- 
based machine guidance at the face involves the 
integration or fusion of the data from each of the systems, 



and the utilization of the most accurate readings to update 
references for the other systems. For example, the 
gyroscope and not the scanning laser system will probably 
be used for closed-loop control of the heading changes of 
the mining machine, but the laser heading data will be 
used to update the gyroscope's reference periodically to 
compensate for drift. Because the gyroscope and laser 
system are being developed on different computers and the 
data must be processed at the same time, the need for a 
computer network is obvious. Closed-loop position and 
heading control of the test bed mining machine was 
achieved in November 1988 over a limited range of angle 
and distance using a single scanning laser and three 
targets. In October, the gyroscope demonstrated heading 
control of the machine over a full 360° range. The 
integrated navigational and guidance system concepts are 
shown in figure 5. 

Because the sheer physical size and expense of mining 
equipment makes continuous testing using this equipment 
unattractive and uneconomical, and because the navigation 






11 




Figure 5.-lntegrated navigational and guidance system concepts. 



and guidance research will not be limited to a single 
vehicle, the Bureau conceptualized an all-purpose vehicle, 
a locomotion emulator (LE), that could carry sensing 
systems for testing. It would use the same command set 
as the target vehicle for which the systems and control 
software were being developed. 

Such an all-purpose vehicle has been built by the Field 
Robotics Center of the Robotics Institute of CMU. As 
figure 6 shows, the LE consists of a three-wheel-set vehicle 
with all wheel sets being driven and steerable, a rotating 
table for the mounting of sensors and/or mockups of 
machine structures, and two computers. The computers 
handle motor control, communications, and the algorithm 



processing that enable the LE to emulate any of the 
following configurations: skid steered, articulated, and 
Ackerman-steered (automobile). Additionally, it can be 
set up to go to any position and heading from an arbitrary 
start (unicycle configuration) and can be joystick-controlled 
through keyboard or joystick for easy positioning. All 
relevant vehicle variables are parameterized and selectable, 
including the introduction of random inaccuracies to 
imitate slippage. The LE at the METF will function as the 
Bureau's primary physical test vehicle in simulated mine 
geometries for the testing of sensors and control software 
for machine guidance and navigation prior to their 
installation on real machinery. 



12 




Figure 6.-Locomotion emulator. 



COAL INTERFACE DETECTION 



BACKGROUND 



ACTIVITIES AND STATUS 



Of equal importance to lateral guidance, and of more 
immediate application, is the task of developing technology 
that automatically maintains the coal cutting geometry to 
that desired. Simply stated, the objective is to keep the 
cutting head in coal no matter what geology is encoun- 
tered. Coal seams vary in pitch and thickness, and may 
have varying characteristics because of the surrounding 
strata. No single coal interface detection scheme will 
suffice; it will take the intelligent interpretation of data 
from a suite of sensors, each operating on different 
principles for each of the differing strata characteristics, to 
keep the cutting head in coal. 

Many techniques have been proposed and tried without 
success. The only technique that is commercially available 
is the natural gamma developed by British Coal. This 
system works well in the appropriate geologies, but unfor- 
tunately not in all. The Bureau believes that all earlier 
efforts failed because the fundamental properties of the 
strata were not thoroughly investigated. Additionally, 
advances in technology have provided several methods that 
were not available to earlier researchers. The research 
effort is described in more detail in reference 6. 



Studies are being conducted on the fundamental 
properties of the strata adjoining the roof and floor in 
several different coal seams. The fundamental properties 
are those measurable aspects of coal and strata that are 
useful for distinguishing between the two by using instru- 
mentation. The goal is to understand those properties and 
use them for the general solution of the coal-interface 
detection problem. 

There have been advances in the technology for 
discriminating among differing electrical signals. The 
electrical signals could be generated by accelerometers 
that measure mining machine vibration and seismic 
vibrations in coal or adjoining strata. The Bureau is 
investigating whether the differences in these vibrational 
signals produced by cutting coal or cutting into the 
adjoining strata are significant and consistent enough to 
allow classification using the advanced discrimination and 
classification techniques (7). If this is feasible, the class- 
ification can then form a means to detect when the mining 
machine starts to cut into the adjoining strata and thus 
provide a controlling signal to adjust the cutting height. 
The few experiments that have been tried so far show 



that there is promise for this technique. For any given 
mining situation, the classification system would be "taught" 
the difference between the signals by purposeful cutting of 
coal and the adjoining floor and roof. 

Another area of active investigation is the use of an 
infrared imaging video camera that responds to fractional 
differences in temperatures by using different colors. Ex- 
periments have recently shown that there is a detectable 
difference in cutting bit and dust temperature depending 
on whether artificial coal or a concrete cap rock is being 
cut. These differences remain even in the presence of wa- 
ter sprays. A system for constant monitoring of the video 
images could effectively be used to control the cutting. 

New developments in radar technology are being 
investigated with the hope that coal strata and coal-air 



13 



interfaces can be detected and measured. Not only would 
this technique help in vertical guidance, it would provide 
a means to measure rib thickness in highwall mining. Rib 
thickness is the primary measurement needed for the 
lateral guidance of highwall mining machines. 

Another method being tried is the use of strata probing 
drills for indicating the difference between coal and strata, 
or coal and air in the case of rib thickness. Precise 
measurement of torque versus penetration distance may 
provide the necessary data for cutting control. In the long 
run, multiple sensor systems will be needed. The data will 
be fed into a powerful computer that filters the data and 
indicates the best estimate of the location of the coal 
interface or coal thickness. 



MACHINE DIAGNOSTICS 



BACKGROUND 

The downtime of a mining machine during production 
is costly today and it will become even more costly with 
computer-assisted machines since a more productive and 
expensive machine is involved. Much downtime is due to 
breakdowns that could have been prevented by early 
detection and immediate attention. Without humans in the 
near vicinity of the computerized mining machines, the 
detection of malfunctions or deteriorating components 
must use sensors. The data from these sensors must be 
processed by a computer in real time and involve little or 
no human interaction in acquisition, analysis, and 
interpretation. The final result will be a recommendation 
by the computer to a human for maintenance, or if there 
is a fault, the location of the faulty part and a procedure 
for its replacement. The nature of the problem suggests 
the utilization of expert systems that use sensor data as 
input. 

The major problems encountered in dealing with expert 
systems are selecting of an appropriate expert system 
method, finding an expert system development tool that 
can utilize sensor data and do so in real time, acquiring 
the knowledge from human experts, and coding this 
knowledge into the expert system knowledge base. Much 
of the data used by humans for diagnosis are obtained by 
hearing and feeling, the two senses and processing tech- 
niques that are not readily available in electromechanical 
sensors and computers. When taken much beyond the 
elementary level, the expert system must use sensor data 
that are machine system specific; such data are not 
available from experts and may have to be empirically 
obtained. 

Three machine subsystems are involved: hydraulic, 
electrical, and mechanical. The initial approach has been 
to utilize a sensor-based expert system for hydraulic system 
component fault detection, and to develop an electrical 
system fault diagnostic system based solely on human input 
of data in response to questions. 



ACTIVITIES AND STATUS 

A prototype hydraulic diagnostic expert system (8) is 
being built using Goldworks, an expert system devel- 
opment environment. The advantage of Goldworks is that 
it not only allows rules for knowledge representation, but 
it is a frame-based system that allows a frame network to 
be set up that can model a hierarchy of objects and the 
relationships among these objects. In this case, a frame 
network has been set up to model the hydraulic system 
circuits, components, and sensor information, and their 
relationships. The hydraulic frame network stores infor- 
mation descriptive of the hydraulic system and can accept 
new and variable information from sensors or the human 
operator. The diagnostic rules will in turn digest this 
information and produce a diagnosis if a system malfunc- 
tion exists. Goldworks is also an attractive package 
because it runs on higher level PC's (286- or 386-based 
systems). Although it is written in LISP, it can interface 
with higher level languages such as C and can also 
interface with widely used data base and spreadsheet data 
files. At present, the hydraulic frame network and the 
diagnostic rules for the main, pilot, and five functional 
hydraulic circuits have been completed. This knowledge 
will undergo review by the domain expert and mine main- 
tenance experts for validation. There are presently 18 
sensors installed on the test bed miner that either char- 
acterize the hydraulic system (pressure, flow, temperature, 
level) or reveal the state of action of the miner. The next 
step is to complete the group of sensors for hydraulic 
system characterization and design an interface linking the 
sensor data to the diagnostic expert system through an 
onboard data acquisition and control system. Finally, the 
expert system will be validated and evaluated by inducing 
faults into the system and allowing the diagnostic knowl- 
edge base and sensor data to produce system diagnoses. 

A different approach was taken for an expert system 
to help troubleshoot the electrical system of a mining 
machine (9). The objective was to produce an interactive 



14 



troubleshooting aid to help or train maintenance personnel 
in the identification of control malfunctions in the pump, 
tram, conveyor, and cutting electrical circuits. It uses 
Level 5 as the expert system development tool. Graphical 
displays have been utilized to help the user identify points 
of electrical measurement and location of parts. The pro- 
totype system has been used by untrained personnel to 
locate six induced faults in the electrical system of the 



Joy 16CM. Serious limitations with the Level 5 tool have 
been encountered: the specifics of the machine are buried 
within rules that make adaptation to other machines 
difficult, and the ordering of the rules drastically affects 
the apparent intelligence and efficiency in locating faulty 
components. An effort is underway to find a more suitable 
expert system tool and to encapsulate the whole system 
into a mineworthy form for on machine installation. 



PLANNING 



BACKGROUND 

Planning is the major element that is responsible for 
machine intelligence— the ability of the machine to make 
decisions autonomously, as do humans, based on an anal- 
ysis of current circumstances in the context of the job to 
be performed. It represents the most complex of research 
issues. Planning takes place at many levels in the hierar- 
chical control system. At the lowest level, the planning 
may determine the elemental moves to change the location 
of a machine without crashing into the ribs or pillars. At 
a higher level, planning may determine the sequence of 
positions that the machine must reach to mine 40 ft down 
an entry or to move to a different entry. At even higher 
levels, it may involve the planning of entries to avoid a clay 
vein that is known to exist from survey data. At all levels, 
planning involves input data, whether from sensors or a 
data base; it involves a representation of that data and a 
context for its interpretation; and it involves the decom- 
position and sequencing of tasks whether they are defining 
goals, subgoals, or machine commands. Figure 2 indicates 
the extent of this issue. 



The task of planning research includes defining the 
appropriate levels and the means to represent and contain 
the knowledge. The decomposition of the tasks for com- 
puter control of a machine is highly machine dependent 
and requires indepth knowledge of mining and machine 
operating techniques. The computer environment and 
human interface must be designed to be able to accept 
new knowledge as it is accumulated by the observation of 
the machines and to allow human intervention when they 
get into circumstances beyond their intellectual capabilities. 

ACTIVITIES AND STATUS 

At this point in the development of computer-assisted 
mining machines, there is little more than a recognition 
that this research must be done. As mentioned in the 
"Fundamental Research" section, both CMU and NIST are 
actively pursuing research in this area for the Bureau. 
During the next year, once the mining machine motion 
can be controlled through guidance system sensors, the 
development of path planning software will begin at the 
Bureau. 



15 



SUMMARY 



The U.S. Bureau of Mines is committed to research 
leading to fundamental technologies that will allow the 
evolutionary development of computer-assisted mining 
systems for underground coal mines. The resulting relo- 
cation of the equipment operators to a secure, remote 
location underground will substantially reduce worker 
exposure to face hazards— falls of roof, equipment acci- 
dents, dust and noise, and explosions-with a resultant 
drastic lowering of the incident rates of injuries, deaths, 
and health problems. 

This report has described the major elements of this 
research and how these elements were selected. The 
status of the research in each of the major areas has been 
presented, showing the direction being taken and the level 
of advancement. Some vital issues were not discussed such 
as the need for substantial industry cooperation in 
providing a site for underground testing of prototype 
machinery, and for providing detailed knowledge of mining 
techniques, and the cooperation of the machine manu- 
facturers in providing a suitable machine for modification 
and testing. The issue of permissibility and modifications 
to the health and safety regulations was not discussed and 
the discussion of intelligent machine action planning, 
although touched upon, was incomplete out of necessity. 



The Bureau's approach is to obtain a complete repre- 
sentation of the research issues from the top down and 
conduct its development of prototype systems from the 
bottom up. 

At this point, the appendages of a continuous mining 
machine have been brought under computer control. A 
computer system network has been defined and links to 
heterogeneous computers established; a multiple sensor- 
based navigation and guidance system has been concep- 
tualized, hardware has been purchased, and software is 
being developed and evaluated. A system view port and 
manual control console have been developed on a Sun 
4/110 that serve to log sensor data and facilitate the 
testing of guidance sensor locations and machine moves 
in software. An all-purpose vehicle emulator is built and 
ready for physical testing of guidance systems. Prototype 
expert systems for hydraulic and electrical system 
diagnostics have been developed. The basic principles of 
coal-interface detection are being investigated, and some 
are showing promising results. Object-oriented language 
is being investigated as a tool for rapid prototyping of 
intelligent planning. 



REFERENCES 



1. Simpson, J. A., R. J. Hocken, and J. S. Albus. The Automated 
Manufacturing Research Facility of the National Bureau of Standards. 
J. Manufacturing Systems, v. 1, 1983, p. 17. 

2. Albus, J. S., H. G. McCain, and R Lumia. NASA/NBS Standard 
Reference Model for Telerobot Control System Architecture 
(NASREM). NBS Tech. Note 1235, 1987. 

3. Sammarco, J. J. Closed Loop Control for a Continuous Mining 
Machine. BuMines RI 9209, 1988, 17 pp. 

4. Schiffbauer, W. H. A Testbed for Autonomous Mining Machine 
Experiments. BuMines IC 9198, 1988, 20 pp. 

5. Anderson, D. L. Position and Heading Determination of a 
Continuous Mining Machine Using an Angular Position-Sensing System. 
IC 9222, 1989, 8 pp. 

6. Dobroski, H., Jr. The Application of Coal Interface Detection 
Techniques for Robotized Continuous Mining Machines. Paper in 



Proceedings of the Ninth WVU International Coal Mine Electrotech- 
nology Conference. WV Univ., Morgantown, WV, 1988, pp. 223-228. 

7. Mowrey, G. L. Applying Adaptive Signal Discrimination Systems 
to Mining Problems. Paper in Proceedings of the Ninth WVU 
International Coal Mine Electrotechnology Conference. WV Univ., 
Morgantown, WV, 1988, pp. 59-64. 

8. Mitchell, J. A Knowledge-Based System for Hydraulic 
Maintenance of a Continuous Miner. Paper in Proceedings of the 
Ninth WVU International Coal Mine Electrotechnology Conference. 
WV Univ., Morgantown, WV, 1988, pp. 95-100. 

9. Berzonsky, B. E. A Knowledge-Based Electrical Diagnostic 
System for Mining Machine Maintenance. Paper in Proceedings of the 
Ninth WVU International Coal Mine Electrotechnology Conference. 
WV Univ., Morgantown, WV, 1988, pp. 89-94. 



U.S. GOVERNMENT PRINTING OFFICE: 611-012/00,102 



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